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Where used as subflooring or combination subfloor underlayment, wood structural panels shall be of one of the grades specified in Table R503.2.1.1(1). Where sanded plywood is used as combination subfloor underlayment, the grade, bond classification, and Performance Category shall be as specified in Table R503.2.1.1(2).
TABLE R503.2.1.1(1)
ALLOWABLE SPANS AND LOADS FOR WOOD STRUCTURAL PANELS FOR ROOF AND SUBFLOOR SHEATHING AND COMBINATION SUBFLOOR UNDERLAYMENTa, b, c
SPAN RATING MINIMUM NOMINAL PANEL THICKNESS (inch) ALLOWABLE LIVE LOAD (psf)h, I MAXIMUM SPAN (inches) LOAD (pounds per square foot, at maximum span) MAXIMUM SPAN (inches)
SPAN @ 16" o.c. SPAN @ 24" o.c. With edge supportd Without edge support Total load Live load
Sheathinge     Rooff Subfloorj
16/0
3/8 30 16 16 40 30 0
20/0
3/8 50 20 20 40 30 0
24/0
3/8 100 30 24 20g 40 30 0
24/16
7/16 100 40 24 24 50 40 16
32/16
15/32, 1/2 180 70 32 28 40 30 16h
40/20
19/32, 5/8 305 130 40 32 40 30 20h, i
48/24
23/32, 3/4 175 48 36 45 35 24
60/32
7/8 305 60 48 45 35 32
Underlayment,
C-C plugged, single floore
    Rooff Combination subfloor underlaymentk
16 o.c.
19/32, 5/8 100 40 24 24 50 40 16i
20 o.c.
19/32, 5/8 150 60 32 32 40 30 20i, j
24 o.c.
23/32, 3/4 240 100 48 36 35 25 24
32 o.c.
7/8 185 48 40 50 40 32
48 o.c.
13/32, 11/8 290 60 48 50 40 48
For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
  1. The allowable total loads were determined using a dead load of 10 psf. If the dead load exceeds 10 psf, then the live load shall be reduced accordingly.
  2. Panels continuous over two or more spans with long dimension (strength axis) perpendicular to supports. Spans shall be limited to values shown because of possible effect of concentrated loads.
  3. Applies to panels 24 inches or wider.
  4. Lumber blocking, panel edge clips (one midway between each support, except two equally spaced between supports where span is 48 inches), tongue-and-groove panel edges, or other approved type of edge support.
  5. Includes Structural I panels in these grades.
  6. Uniform load deflection limitation: 1/180 of span under live load plus dead load, 1/240 of span under live load only.
  7. Maximum span 24 inches for 15/32- and 1/2-inch panels.
  8. Maximum span 24 inches where 3/4-inch wood finish flooring is installed at right angles to joists.
  9. Maximum span 24 inches where 1.5 inches of lightweight concrete or approved cellular concrete is placed over the subfloor.
  10. Unsupported edges shall have tongue-and-groove joints or shall be supported with blocking unless minimum nominal 1/4-inch-thick wood panel-type underlayment, fiber-cement underlayment with end and edge joints offset not less than 2 inches or 11/2 inches of lightweight concrete or approved cellular concrete is placed over the subfloor, or 3/4-inch wood finish flooring is installed at right angles to the supports. Fiber-cement underlayment shall comply with ASTM C1288 or ISO 8336 Category C. Allowable uniform live load at maximum span, based on deflection of 1/360 of span, is 100 psf.
  11. Unsupported edges shall have tongue-and-groove joints or shall be supported by blocking unless nominal 1/4-inch-thick wood panel-type underlayment, fiber-cement underlayment with end and edge joints offset not less than 2 inches or 3/4-inch wood finish flooring is installed at right angles to the supports. Fiber-cement underlayment shall comply with ASTM C1288 or ISO 8336 Category C. Allowable uniform live load at maximum span, based on deflection of 1/360 of span, is 100 psf, except panels with a span rating of 48 on center are limited to 65 psf total uniform load at maximum span.
  12. Allowable live load values at spans of 16 inches on center and 24 inches on center taken from referenced standard APA E30, APA Engineered Wood Construction Guide. Refer to referenced standard for allowable spans not listed in the table.
ALLOWABLE SPANS FOR SANDED
PLYWOOD COMBINATION SUBFLOOR UNDERLAYMENTa
IDENTIFICATION SPACING OF JOISTS (inches)
16 20 24
Species groupb
1
1/2 5/8 3/4
2, 3
5/8 3/4 7/8
4
3/4 7/8 1
For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.
  1. Plywood continuous over two or more spans and face grain perpendicular to supports. Unsupported edges shall be tongue-and-groove or blocked except where nominal 1/4-inch-thick wood panel-type underlayment, fiber-cement underlayment or 3/4-inch wood finish floor is used. Fiber-cement underlayment shall comply with ASTM C1288 or ISO 8336 Category C. Allowable uniform live load at maximum span based on deflection of 1/360 of span is 100 psf.
  2. Applicable to all grades of sanded exterior-type plywood.

Related Code Sections

R503.2.1.1 Floors, Subfloor and Combined Subfloor Underlayment
Where used as subflooring or combination subfloor underlayment, wood structural panels shall be of one of the grades specified in Table R503.2.1.1(1 ...